Clinical manifestations of typhoid fever Week 1 • Rising fever • Bacteremia • Relative bradycardia (pulse-temperature dissociation) Week 2 • Abdominal pain • Rose spots on trunk & abdomen Week 3 • Hepatosplenomegaly • Intestinal bleeding & perforation Typhoid fever is a life-threatening infection caused by Salmonella Typhi or Paratyphi. These gram-negative, enteric pathogens reside only in the gastrointestinal tract of humans

Choice B: . Transmission occurs via the fecal-oral route, primarily due to ingestion of food or water contaminated by human feces. Therefore, most cases arise in the developing world where sanitation is poor. Travelers who have not been vaccinated (with typhoid vaccine) are at risk and may return clinically ill. Typhoidal Salmonella species invade enterocytes, travel from the apical to the basolateral end of the cell in vacuoles, and emerge in the intestinal submucosa. Here, the organism is phagocytosed by macrophages but is able to evade destruction due to a specialized capsular antigen (Vi) that impairs the macrophage-mediated oxidative burst. The pathogen subsequently replicates in an unchecked fashion within macrophages and spreads through the lymphatic and reticuloendothelial system, leading to widespread, systemic illness. Manifestations typically develop over weeks in a step-wise fashion. Patients usually develop a progressive fever, often with relative bradycardia (pulse-temperature dissociation), followed by abdominal pain, salmon-colored macules on the trunk ("rose spots"), and constipation or diarrhea. Dissemination through the reticuloendothelial system often causes hepatosplenomegaly, anemia, and leukopenia. Later, ulceration of Peyer patches (lymphoid aggregations in the small intestine submucosa) can result in gastrointestinal bleeding or intestinal perforation. Antibiotic treatment is required to prevent complications and death.

Choice A: Malaria is transmitted by the bite of the female Anopheles mosquito and typically causes paroxysmal fever with nonspecific symptoms (eg, chills, fatigue, headache, myalgias). However, the fever is almost always associated with tachycardia (not bradycardia), and peripheral blood smear will usually demonstrate the parasite and/or signs of red blood cell lysis.

Choice D: Meningococcal meningitis is transmitted by aerosolized droplets from a carrier or infected patient and is associated with rapid-onset confusion, sepsis, hypotension, and a petechial/purpuric rash.

Choice E: Treponema pallidum , the spirochete that causes syphilis, is transmitted sexually. Secondary syphilis is usually characterized by a widespread maculopapular rash that involves the palms and soles, generalized lymphadenopathy, and constitutional symptoms such as fever, headache, and myalgias. This patient's pulse-temperature dissociation, limited rash, and lack of adenopathy make syphilis less likely than typhoid fever.

Educational Objective: Typhoid fever is caused by Salmonella Typhi or Paratyphi and presents with escalating fever, followed by abdominal pain, formation of rose spots on the chest/abdomen, and hemorrhagic enteritis with possible bowel perforation. Humans are the only reservoir; transmission is fecal-oral and primarily occurs due to ingestion of food or water contaminated with feces. Microbiology

USMLE Question Bank

USMLE Question Bank